U.S. patent application number 12/766508 was filed with the patent office on 2011-02-10 for display driver circuit and display device.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to In-Suk KIM, Jae-Goo LEE.
Application Number | 20110032279 12/766508 |
Document ID | / |
Family ID | 43534506 |
Filed Date | 2011-02-10 |
United States Patent
Application |
20110032279 |
Kind Code |
A1 |
KIM; In-Suk ; et
al. |
February 10, 2011 |
DISPLAY DRIVER CIRCUIT AND DISPLAY DEVICE
Abstract
A display driver circuit and a display device are provided. The
display driver circuit may have positive and negative resistor
strings that are symmetrically formed and include a plurality of
resistors, and applies a gamma voltage to one of the positive and
negative resistor strings in response to a polarity selection
signal, thereby generating and outputting a positive grayscale
voltage and a negative grayscale voltage.
Inventors: |
KIM; In-Suk; (Suwon-si,
KR) ; LEE; Jae-Goo; (Yongin-si, KR) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Suwon-si
KR
|
Family ID: |
43534506 |
Appl. No.: |
12/766508 |
Filed: |
April 23, 2010 |
Current U.S.
Class: |
345/690 ;
345/89 |
Current CPC
Class: |
G09G 2330/021 20130101;
G09G 2320/0276 20130101; G09G 2320/0252 20130101; G09G 3/3696
20130101; G09G 3/2007 20130101 |
Class at
Publication: |
345/690 ;
345/89 |
International
Class: |
G09G 5/10 20060101
G09G005/10 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 5, 2009 |
KR |
10-2009-0072092 |
Claims
1. A display driver circuit, comprising: a reference voltage
selection unit configured to receive and divide a first supply
voltage and a second supply voltage, and select and output a
maximum reference voltage and a minimum reference voltage; and a
grayscale voltage generator including a gamma voltage selector
configured to receive the maximum and minimum reference voltages,
generate at least two gamma voltages by dividing the maximum and
minimum reference voltages, and generate, using the at least two
gamma voltages, at least two positive grayscale voltages that range
from the minimum reference voltage to the maximum reference voltage
or at least two negative grayscale voltages that range from the
maximum reference voltage to the minimum reference voltage, wherein
an absolute value of a difference between a first positive
grayscale voltage and a second positive grayscale voltage of the at
least two positive grayscale voltages equals an absolute value of a
difference between a first negative grayscale voltage and a second
negative grayscale voltage of the at least two negative grayscale
voltages.
2. The display driver circuit according to claim 1, wherein the
reference voltage selection unit includes: a first resistor string
including a plurality of first resistors connected in series
between the first and second supply voltages and configured to
divide the first and second supply voltages; a maximum reference
voltage selector configured to select a first voltage divided by
the first resistor string in response to a maximum reference
voltage selection signal, and output the first voltage as the
maximum reference voltage; a minimum reference voltage selector
configured to select a second voltage divided by the first resistor
string that is lower than the maximum reference voltage in response
to a minimum reference voltage selection signal, and output the
second voltage as the minimum reference voltage; a first reference
buffer configured to receive and buffer the maximum reference
voltage and output a maximum gamma voltage from among the at least
two gamma voltages; and a second reference buffer configured to
receive and buffer the minimum reference voltage and output a
minimum gamma voltage from among the at least two gamma
voltages.
3. The display driver circuit according to claim 2, wherein the
gamma voltage selector includes: a gamma voltage generator
configured to receive the maximum and minimum gamma voltages and
generate the at least two gamma voltages by dividing the maximum
and minimum gamma voltages in response to one or more gamma
selection signals; a resistor selector configured to apply the at
least two gamma voltages to corresponding nodes among a plurality
of nodes of a resistor string selected from a positive resistor
string and a negative resistor string in response to a polarity
selection signal; a resistor string unit including the positive
resistor string and the negative resistor string that receive the
at least two gamma voltages at corresponding nodes, and
respectively generate the at least two positive grayscale voltages
having sequentially increasing levels and the at least two negative
grayscale voltages having sequentially decreasing levels by
dividing the at least two gamma voltages; and a grayscale voltage
selector configured to receive the at least two positive grayscale
voltages and the at least two negative grayscale voltages from the
resistor string selected from the positive resistor string and the
negative resistor string in response to the polarity selection
signal, and output a selection grayscale voltage.
4. The display driver circuit according to claim 3, wherein the
gamma voltage generator includes: a second resistor string
including a plurality of second resistors connected in series
between the maximum and minimum gamma voltages and configured to
divide the maximum and minimum gamma voltages; and a gamma
selection unit configured to select at least one gamma voltage
divided by the second resistor string in response to the one or
more gamma selection signals and output the at least one selected
gamma voltage.
5. The display driver circuit according to claim 4, wherein the
gamma selection unit includes at least one gamma selector
configured to select one of voltages divided by the second resistor
string in response to a corresponding gamma selection signal of the
at least one gamma selection signal.
6. The display driver circuit according to claim 3, wherein the
positive resistor string includes a plurality of third resistors
connected in series, and is configured to receive the at least two
gamma voltages and generate the at least two positive grayscale
voltages by dividing the at least two gamma voltages.
7. The display driver circuit according to claim 6, wherein the
negative resistor string includes a plurality of fourth resistors
having the same resistance as the plurality of third resistors,
connected in series, and disposed in the reverse order of the third
resistors, and is configured to receive the at least two gamma
voltages and generate the at least two negative grayscale voltages
by dividing the at least two gamma voltages.
8. The display driver circuit according to claim 3, wherein the
resistor selector includes: a first polarity selector configured to
apply the maximum gamma voltage to a first end of the resistor
string selected from the positive resistor string and the negative
resistor string in response to the polarity selection signal; a
second polarity selector configured to apply the minimum gamma
voltage to a second end of the resistor string selected from the
positive resistor string and the negative resistor string in
response to the polarity selection signal; and a gamma selection
buffer unit configured to receive at least two gamma voltages and
output the at least two gamma voltages to corresponding nodes of
the resistor string selected from the positive resistor string and
the negative resistor string in response to the polarity selection
signal.
9. The display driver circuit according to claim 8, wherein the
gamma selection buffer unit includes at least two gamma selection
buffers each configured to receive, buffer and output a
corresponding one of the at least two gamma voltages to a
corresponding node of the resistor string selected from the
positive resistor string and the negative resistor string in
response to the polarity selection signal.
10. The display driver circuit according to claim 9, wherein each
of the at least two gamma selection buffers includes: a first
amplifier configured to receive the corresponding one of the at
least two gamma voltages and a feedback voltage, sense and amplify
a difference between the corresponding one of the at least two
gamma voltages and the feedback voltage, and output the amplified
difference; two second amplifiers configured to receive and buffer
the output of the first amplifier, output a corresponding grayscale
voltage to corresponding nodes of the positive resistor string and
the negative resistor string, and apply the corresponding grayscale
voltage to the first amplifier as the feedback voltage; and a
switch configured to transfer the output of the first amplifier to
one of the two second amplifiers in response to the polarity
selection signal.
11. The display driver circuit according to claim 3, wherein the
grayscale voltage generator further includes a common voltage
generator configured to generate and output at least one of a first
common voltage that is lower than the minimum gamma voltage and a
second common voltage that is higher than the maximum gamma voltage
in response to the polarity selection signal.
12. The display driver circuit according to claim 11, wherein the
grayscale voltage generator further includes: a reference voltage
selection register configured to output the maximum and minimum
reference voltage selection signals; a gamma selection register
configured to output the one or more gamma selection signals; and a
polarity selection register configured to output the polarity
selection signal in response to a polarity signal.
13. The display driver circuit according to claim 12, further
comprising: a controller configured to output a source driver
control signal, a gate driver control signal, and the polarity
signal in response to image data and a command; a source driver
configured to receive the selection grayscale voltage in response
to the source driver control signal, and apply a display data
voltage to data lines of a display panel; and a gate driver
configured to apply a gate-on voltage to gate lines of the display
panel in response to the gate driver control signal.
14. A display device comprising: a panel including an array
substrate including a plurality of pixel electrodes between a
plurality of data lines and a plurality of gate lines, a counter
substrate disposed to face the array substrate and including at
least one common electrode, and a liquid crystal layer interposed
between the array substrate and the counter substrate; a controller
configured to output a source driver control signal, a gate driver
control signal, and a polarity signal in response to image data and
a command; a grayscale voltage generator configured to output a
selection grayscale voltage in response to the polarity signal; a
source driver configured to receive the selection grayscale voltage
in response to the source driver control signal and apply a display
data voltage to the plurality of data lines; and a gate driver
configured to apply a gate-on voltage to the plurality of gate
lines in response to the gate driver control signal, wherein the
grayscale voltage generator includes: a reference voltage selection
unit configured to receive and divide a first supply voltage and a
second supply voltage, and select and output a maximum reference
voltage and a minimum reference voltage; and a gamma voltage
selector configured to receive the maximum and minimum reference
voltages, generate at least two gamma voltages by dividing the
maximum and minimum reference voltages, and generate at least two
positive grayscale voltages that range from the minimum reference
voltage to the maximum reference voltage or at least two negative
grayscale voltages that range from the maximum reference voltage to
the minimum reference voltage using the at least two gamma
voltages, wherein an absolute value of a difference between a first
positive grayscale voltage and a second positive grayscale voltage
of the at least two positive grayscale voltages equals an absolute
value of a difference between a first negative grayscale voltage
and a second negative grayscale voltage of the at least two
negative grayscale voltages.
15. The display panel according to claim 14, wherein the reference
voltage selection unit includes: a first resistor string including
a plurality of first resistors connected in series between the
first and second supply voltages and configured to divide the first
and second supply voltages; a maximum reference voltage selector
configured to select a first voltage divided by the first resistor
string in response to a maximum reference voltage selection signal,
and output the first voltage as the maximum reference voltage; a
minimum reference voltage selector configured to select a second
voltage divided by the first resistor string that is lower than the
maximum reference voltage in response to a minimum reference
voltage selection signal, and output the second voltage as the
minimum reference voltage; a first reference buffer configured to
receive and buffer the maximum reference voltage and output a
maximum gamma from among the at least two gamma voltages; and a
second reference buffer configured to receive and buffer the
minimum reference voltage and output a minimum gamma voltage from
among the at least two gamma voltages.
16. The display panel according to claim 15, wherein the gamma
voltage selector includes: a gamma voltage generator configured to
receive the maximum and minimum gamma voltages and generate the at
least two gamma voltages by dividing the maximum and minimum gamma
voltages in response to one or more gamma selection signals; a
resistor selector configured to apply the at least two gamma
voltages to corresponding nodes among a plurality of nodes of a
resistor string selected from a positive resistor string and a
negative resistor string in response to a polarity selection
signal; a resistor string unit including the positive resistor
string and the negative resistor string that receive the at least
two gamma voltages at corresponding nodes, and respectively
generate the at least two positive grayscale voltages having
sequentially increasing levels and the at least two negative
grayscale voltages having sequentially decreasing levels by
dividing the at least two gamma voltages; and a grayscale voltage
selector configured to receive the at least two positive grayscale
voltages and the at least two negative grayscale voltages from the
resistor string selected from the positive resistor string and the
negative resistor string in response to the polarity selection
signal, and output the selection grayscale voltage.
17. The display panel according to claim 16, wherein the gamma
voltage generator includes: a second resistor string having a
plurality of second resistors connected in series between the
maximum and minimum gamma voltages and configured to divide the
maximum and minimum gamma voltages; and a gamma selection unit
configured to select at least one gamma voltage divided by the
second resistor string in response to the one or more gamma
selection signals and output the at least one selected gamma
voltage.
18. The display panel according to claim 16, wherein the positive
resistor string includes a plurality of third resistors connected
in series, and is configured to receive the at least two gamma
voltages and generate the at least two positive grayscale voltages
by dividing the at least two gamma voltages.
19. The display panel according to claim 18, wherein the negative
resistor string includes a plurality of fourth resistors having the
same resistance as the plurality of third resistors, connected in
series, and disposed in the reverse order of the third resistors,
and is configured to receive the at least two gamma voltages and
generate the at least two negative grayscale voltages by dividing
the at least two gamma voltages.
20. The display panel according to claim 16, wherein the resistor
selector includes: a first polarity selector configured to apply
the maximum gamma voltage to a first end of the resistor string
selected from the positive resistor string and the negative
resistor string in response to the polarity selection signal; a
second polarity selector configured to apply the minimum gamma
voltage to a second end of the resistor string selected from the
positive resistor string and the negative resistor string in
response to the polarity selection signal; and a gamma selection
buffer unit configured to receive at least two gamma voltages and
output the at least two gamma voltages to corresponding nodes of
the resistor string selected from the positive resistor string and
the negative resistor string in response to the polarity selection
signal.
Description
PRIORITY STATEMENT
[0001] This application claims priority from Korean Patent
Application No. 10-2009-0072092, filed on Aug. 5, 2009, the
contents of which are hereby incorporated herein by reference in
its entirety.
BACKGROUND
[0002] One or more exemplary embodiments relate to a display driver
circuit and display device, and more particularly, to a display
driver circuit outputting symmetrical grayscale voltages at high
speed and low power consumption and a display device.
SUMMARY
[0003] One or more exemplary embodiments provide a display driver
circuit that outputs symmetrical grayscale voltages at high speed
and low power consumption.
[0004] According to an aspect of an exemplary embodiment, there is
provided a display driver circuit, the display driver circuit
including: a reference voltage selection unit configured to receive
and divide first supply voltage and a second supply voltage, and
select and output a maximum reference voltage and a minimum
reference voltage; and a grayscale voltage generator including a
gamma voltage selector configured to receive the maximum and
minimum reference voltages, generate at least two gamma voltages by
dividing the maximum and minimum reference voltages, and generate,
using the at least two gamma voltages, at least two positive
grayscale voltages that range from the minimum reference voltage to
the maximum reference voltage or at least two negative grayscale
voltages that range from the maximum reference voltage to the
minimum reference voltage. Here, a difference between a first
positive grayscale voltage and a second positive grayscale voltage
of the at least two positive grayscale voltages equals to a
difference between a first negative grayscale voltage and a second
negative grayscale voltage of the at least two negative grayscale
voltages.
[0005] The reference voltage selection unit may include: a first
resistor string including a plurality of first resistors connected
in series between the first and second supply voltages and
configured to divide the first and second supply voltages; a
maximum reference voltage selector configured to select a first
voltage divided by the first resistor string in response to a
maximum reference voltage selection signal, and output the first
voltage as the maximum reference voltage; a minimum reference
voltage selector configured to select a second voltage divided by
the first resistor string that is lower than the maximum reference
voltage in response to a minimum reference voltage selection
signal, and output the second voltage as the minimum reference
voltage; a first reference buffer configured to receive and buffer
the maximum reference voltage, and output a maximum gamma voltage
from among the at least two gamma voltages; and a second reference
buffer configured to receive and buffer the minimum reference
voltage, and output a minimum gamma voltage from among the at least
two gamma voltages.
[0006] The gamma voltage selector may include: a gamma voltage
generator configured to receive the maximum and minimum gamma
voltages and generate the at least two gamma voltages by dividing
the maximum and minimum gamma voltages in response to one or more
gamma selection signals; a resistor selector configured to apply
the at least two gamma voltages to the corresponding nodes among a
plurality of nodes of a resistor string selected from a positive
resistor string and a negative resistor string in response to a
polarity selection signal; a resistor string unit including the
positive resistor string and the negative resistor string that
receive the at least two gamma voltages at the corresponding nodes,
and respectively generate the at least two positive grayscale
voltages having sequentially increasing levels and the at least two
negative grayscale voltages having sequentially decreasing levels
by dividing the at least two gamma voltages; and a grayscale
voltage selector configured to receive the at least two positive
grayscale voltages and the at least two negative grayscale voltages
from the resistor string selected from the positive resistor string
and the negative resistor string in response to the polarity
selection signal, and output a selection grayscale voltage.
[0007] The gamma voltage generator may include a second resistor
string including a plurality of second resistors connected in
series between the maximum and minimum gamma voltages and
configured to divide the maximum and minimum gamma voltages; and a
gamma selection unit configured to select at least one gamma
voltage divided by the second resistor string in response to the
one or more gamma selection signals and output the at least one
selected gamma voltage.
[0008] The positive resistor string may include a plurality of
third resistors connected in series, and may be configured to
receive the at least two gamma voltages and generate the at least
two positive grayscale voltages by dividing the at least two gamma
voltages.
[0009] The negative resistor string may include a plurality of
fourth resistors having the same resistance as the third resistors,
connected in series, and disposed in the reverse order of the third
resistors, and may be configured to receive the at least two gamma
voltages and generate the at least two negative grayscale voltages
by dividing the at least two gamma voltages.
[0010] The resistor selector may include: a first polarity selector
configured to apply the maximum gamma voltage to a first end of the
resistor string selected from the positive resistor string and the
negative resistor string, in response to the polarity selection
signal; a second polarity selector configured to apply the minimum
gamma voltage to a second end of the resistor string selected from
the positive resistor string and the negative resistor string in
response to the polarity selection signal; and a gamma selection
buffer unit configured to receive at least two gamma voltages and
output the at least two gamma voltages to corresponding nodes of
the resistor string selected from the positive resistor sting and
the negative resistor string in response to the polarity selection
signal.
[0011] The grayscale voltage generator may further include a common
voltage generator configured to generate and output at least one of
a first common voltage that is lower than the minimum gamma voltage
and a second common voltage that is higher than the maximum gamma
voltage in response to the polarity selection signal.
[0012] The grayscale voltage generator may further include: a
reference voltage selection register configured to output the
maximum and minimum reference voltage selection signals; a gamma
selection register configured to output the one or more gamma
selection signals; and a polarity selection register configured to
output the polarity selection signal in response to a polarity
signal. The display driver circuit may further include: a
controller configured to output a source driver control signal, a
gate driver control signal, and the polarity signal in response to
image data and a command; a source driver configured to receive the
selection grayscale voltage in response to the source driver
control signal, and apply a display data voltage to data lines of a
display panel; and a gate driver configured to apply a gate-on
voltage to gate lines of the display panel in response to the gate
driver control signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The above and/or other aspects will become apparent and more
readily appreciated from the following description of exemplary
embodiments, with reference to the accompanying drawings in
which:
[0014] FIG. 1 illustrates a display driver circuit according to an
exemplary embodiment.
[0015] FIG. 2 is a graph illustrating symmetrical grayscale
voltages generated from the display driver circuit of FIG. 1.
[0016] FIG. 3 is a circuit diagram of an exemplary gamma selection
buffer shown in FIG. 1.
[0017] FIG. 4 is a block diagram of a display device according to
an example embodiment.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0018] Various exemplary embodiments will now be described more
fully with reference to the accompanying drawings in which some
example embodiments are shown. In the drawings, various aspects
such as the thicknesses of layers and regions may be exaggerated
for clarity. Detailed illustrative embodiments are disclosed
herein. However, specific structural and functional details
disclosed herein are merely representative for purposes of
describing example embodiments. This inventive concept, however,
may be embodied in many alternate forms and should not be construed
as limited to only example embodiments set forth herein.
[0019] Among display devices, a liquid crystal display (LCD)
includes a panel having a plurality of pixel units. Each pixel unit
includes an array substrate on which a switching device and a pixel
electrode are formed, a counter substrate facing the array
substrate and on which a common electrode is formed, and a liquid
crystal layer interposed between the array substrate and the
counter substrate. Each pixel unit controls light transmissivity by
applying an electric field to the liquid crystal layer, thereby
displaying an image. To be specific, the transmissivity of the
liquid crystal layer is controlled by a difference between voltages
applied to the pixel electrode and the common electrode.
[0020] However, when an electric field in one direction is
constantly applied to the liquid crystal layer by voltages applied
to the common electrode and the pixel electrode, the liquid crystal
layer deteriorates. In order to not fix an electric field applied
to a liquid crystal layer in one direction and prevent such a
deterioration of the liquid crystal layer, a display driver circuit
driving the panel of a display device periodically inverts the
polarity of each pixel electrode with respect to a common
electrode. Grayscale voltages with two polarities applied to a
pixel electrode are classified into a positive grayscale voltage
and negative grayscale voltage. A display driver circuit inverts
the polarity of a pixel electrode using dot inversion, line
inversion, frame inversion, etc.
[0021] FIG. 1 illustrates a display driver circuit according to an
exemplary embodiment.
[0022] In FIG. 1, a display driver circuit 100 includes a reference
voltage selection register 110, a reference voltage selection unit
120, a gamma selection register 130, a polarity selection register
140, and a gamma voltage selector 150.
[0023] The reference voltage selection register 110 outputs a
maximum reference voltage selection signal (maxsr) and a minimum
reference voltage selection signal (minsr) to the reference voltage
selection unit 120. The maximum reference voltage selection signal
maxsr and the minimum reference voltage selection signal minsr may
be stored in advance in a maximum reference voltage selection
register and a minimum reference voltage selection register,
respectively, or received from an external source.
[0024] The reference voltage selection unit 120 includes a first
resistor string R-ST1, a maximum reference voltage selector 121, a
minimum reference voltage selector 122, and first and second
reference buffers 123 and 124.
[0025] The first resistor string R-ST1 has a plurality of resistors
connected in series between a first supply voltage VDD and a second
supply voltage VGS, and outputs a plurality of voltages that are
between the first supply voltage VDD and the second supply voltage
VGS.
[0026] The maximum reference voltage selector 121 selects and
outputs a maximum reference voltage Vmax among the voltages output
from the first resistor string R-ST1 in response to the maximum
reference voltage selection signal maxsr output from the reference
voltage selection register 110, and the minimum reference voltage
selector 122 selects and outputs a minimum reference voltage Vmin
among the voltages output from the first resistor string R-ST1 in
response to the minimum reference voltage selection signal minsr
output from the reference voltage selection register 110. At this
time, the maximum reference voltage selector 121 selects a voltage
output between a resistor Rmid disposed in the middle of the
resistors of the first resistor string R-ST1 connected in series
and the first supply voltage VDD and outputs the selected voltage
as the maximum reference voltage Vmax. The minimum reference
voltage selector 122 selects a voltage output between the resistor
Rmid and the second supply voltage VGS and outputs the selected
voltage as the minimum reference voltage Vmin. The maximum and
minimum reference voltage selectors 121 and 122 may be implemented
as multiplexers (MUXs) or decoders.
[0027] The first and second reference buffers 123 and 124 receive
and buffer the maximum and minimum reference voltages Vmax and
Vmin, and output maximum and minimum gamma voltages GVmax and
GVmin, respectively.
[0028] The gamma selection register 130 outputs a plurality of
gamma selection signals (gss). Like the maximum and minimum
reference voltage selection signals maxsr and minsr, the gamma
selection signals gss may be stored in the gamma selection register
130 in advance or received from an external source.
[0029] The polarity selection register 140 outputs a polarity
selection signal (pss) in response to a polarity signal PS. The
polarity signal PS may be received from a controller (not shown) of
a display device, and is a control signal for controlling the
display driver circuit 100 to accurately output positive and
negative grayscale voltages at a predetermined time.
[0030] The gamma voltage selector 150 includes first and second
polarity selectors 151 and 152, a second resistor string R-ST2, a
gamma selection unit 153, a gamma buffer unit 154, positive and
negative resistor strings PR-ST and NR-ST, and a grayscale voltage
selector 155.
[0031] The first polarity selector 151 receives the maximum gamma
voltage GVmax, and applies the maximum gamma voltage GVmax as a
sixty-fourth positive grayscale voltage VP63 or a first negative
grayscale voltage VN0 to one end of the positive resistor string
PR-ST or the negative resistor string NR-ST, respectively, in
response to the polarity selection signal pss applied from the
polarity selection register 140. The second polarity selector 152
receives the minimum gamma voltage GVmin, and applies the minimum
gamma voltage GVmin as a first positive grayscale voltage VP0 or a
sixty-fourth negative grayscale voltage VN63 to the other end of
the positive resistor string PR-ST or the negative resistor string
NR-ST, respectively, in response to the polarity selection signal
pss.
[0032] In one or more exemplary embodiments, it is assumed that the
display driver circuit 100 outputs grayscale voltages with first
and second polarities, and each of the grayscale voltages with
first and second polarities are output as sixty-four grayscale
voltages VP0 to VP63 or VN0 to VN63. Here, it is assumed that the
first-polarity grayscale voltages are positive grayscale voltages,
and the second-polarity grayscale voltages are negative grayscale
voltages. Thus, the maximum reference voltage Vmax output from the
reference voltage selection unit 120 is output as the sixty-fourth
positive grayscale voltage VP63 and the first negative grayscale
voltage VN0, and the minimum reference voltage Vmin is output as
the first positive grayscale voltage VP0 and the sixty-fourth
negative grayscale voltage VN63. However, the number of grayscale
voltages output by the display driver circuit 100 may be adjusted.
When the number of grayscale voltages output by the display driver
circuit 100 is n (where n is a natural number larger than 2), the
maximum voltage Vmax output from the first reference buffer 123 may
be output as an nth positive grayscale voltage VPn-1 and the first
negative grayscale voltage VN0, and the minimum voltage Vmin output
from the second reference buffer 124 may be output as the first
positive grayscale voltage VP0 and an nth negative grayscale
voltage VNn-1.
[0033] The second resistor string R-ST2 has a plurality of
resistors connected in series between the maximum and minimum gamma
voltages GVmax and GVmin and two switches SW1 and SW2, and outputs
a plurality of gamma voltages GV1 to GV9. The two switches SW1 and
SW2 are connected in parallel with resistors disposed at both ends
of the second resistor string R-ST2, and turned on and off in
response to the gamma selection signals gss. That is, as the two
switches SW1 and SW2 are turned on or off, the levels of the gamma
voltages GV1 to GV9 output from the second resistor string R-ST2
vary.
[0034] The gamma selection unit 153 has a plurality of gamma
selectors GS1 to GS9. Each of the gamma selectors GS1 to GS9
selects and outputs one of the gamma voltages GV1 to GV9 output
from the second resistor string R-ST2 in response to the
corresponding one of the gamma selection signals gss. The first to
ninth gamma selectors GS1 to GS9 select the gamma voltages GV1 to
GV9 output from the second resistor string R-ST2 in decreasing
order of voltages. For example, the second gamma selector GS2
selects and outputs gamma voltage GV2 among gamma voltages that are
output from the second resistor string R-ST2, which is less than
the gamma voltage GV1 selected by the first gamma selector GS1.
Similarly, the third gamma selector GS3 selects and outputs gamma
voltage GV3, which is less than gamma voltage GV2 selected by the
second gamma selector GS2, and the ninth gamma selector GS9 selects
and outputs gamma voltage GV9, which is less than the gamma voltage
GV8 selected by the eighth gamma selector GS8. Thus, the gamma
voltages GV1 to GV9 output from the first to ninth gamma selectors
GS1 to GS9 decrease in sequence. Although the gamma selection unit
153 has the nine gamma selectors GS1 to GS9 in FIG. 1, the number
of gamma selectors may vary. The gamma voltages GV1 to GV9 output
from the gamma selection unit 153 are matched to points in the
gamma characteristic curve of a display panel and output. In
particular, most of the gamma voltages GV1 to GV9 are matched to
points adjacent to an inflection point at which the gamma
characteristic curve significantly varies. As the number of gamma
selectors that the gamma selection unit 153 has increases, the
number of gamma voltages output from the gamma selection unit 153
also increases, and thus the gamma voltages approximate the gamma
characteristic curve. The gamma selectors GS1 to GS9 may be
implemented as MUXs or decoders, like the maximum and minimum
reference voltage selectors 121 and 122. However, as the number of
gamma selectors increases, the grayscale voltage selector 150
remarkably increases in size. Thus, the number of gamma selectors
must be appropriately adjusted during design.
[0035] The gamma buffer unit 154 has a plurality of gamma selection
buffers GSB1 to GSB9. The gamma selection buffers GSB1 to GSB9,
numbered the same as the gamma selectors GS1 to GS9, receive the
gamma voltages GV1 to GV9 from the respective corresponding gamma
selectors GS1 to GS9, and buffer and output the gamma voltages GV1
to GV9. In other words, each of the gamma selection buffers GSB1 to
GSB9 corresponds to one of the gamma selectors GS1 to GS9,
receives, buffers and outputs a gamma voltage output from the
corresponding gamma selector. The gamma selection buffer GSB1
buffers the gamma voltage GV1 output from the gamma selector GS1
and outputs the sixty-third positive grayscale voltage VP62 and the
second negative grayscale voltage VN1, and the gamma selection
buffer GSB9 buffers the gamma voltage GV9 output from the gamma
selector GS9 and outputs the second positive grayscale voltage VP1
and the sixty-third negative grayscale voltage VN62. Here, the
second and sixty-third positive grayscale voltages VP1 and VP62 and
the second and sixty-third negative grayscale voltages VN1 and VN62
are output because it is assumed that the display driver circuit
100 outputs sixty-four grayscale voltages. When the number of
output grayscale voltages is n (where n is a natural number larger
than 2), the first gamma selection buffer GSB1 may output an
(n-1)th positive grayscale voltage VPn-2 and the second negative
grayscale voltage VN1, and the ninth gamma selection buffer GSB9
may output the second positive grayscale voltage VP1 and an (n-1)th
negative grayscale voltage VNn-2.
[0036] The positive resistor string PR-ST and the negative resistor
string NR-ST are symmetrical to each other. In the negative
resistor string NR-ST, resistors of the positive resistor string
PR-ST are disposed in the reverse order. To be specific, each of
the positive resistor string PR-ST and the negative resistor string
NR-ST has a plurality of resistors PR1 to PRk or NR1 to NRk, and
two resistors of the same number in the positive resistor string
PR-ST and the negative resistor string NR-ST have the same
resistance.
[0037] The positive resistor string PR-ST and the negative resistor
string NR-ST respectively receives the sixty-fourth positive
grayscale voltage VP63 and the first negative grayscale voltage VN0
from the first polarity selector 151 at one end, and the first
positive grayscale voltage VP0 and the sixty-fourth negative
grayscale voltage VN63 from the second polarity selector 152 at the
other end. Each of the positive resistor string PR-ST and the
negative resistor string NR-ST has the resistors PR1 to PRk or NR1
to NRk connected in series and outputs the positive grayscale
voltages VP1 to VP62 or the negative grayscale voltages VN1 to
VN62. Here, the sixty-fourth positive grayscale voltage VP63 and
the first negative grayscale voltage VN0 applied from the first
polarity selector 151 actually are equal to the maximum gamma
voltage GVmax but are only classified according to whether the
maximum gamma voltage GVmax is applied to the positive resistor
string PR-ST or the negative resistor string NR-ST. Likewise, the
first positive grayscale voltage VP0 and the sixty-fourth negative
grayscale voltage VN63 applied from the second polarity selector
152 actually are equal to the minimum gamma voltage GVmin but are
only classified according to whether the minimum gamma voltage
GVmin is applied to the positive resistor string PR-ST or the
negative resistor string NR-ST.
[0038] In other words, the first and second polarity selectors 151
and 152 select one of the positive resistor string PR-ST and the
negative resistor string NR-ST and apply the maximum and minimum
gamma voltages GVmax and GVmin to both ends of the selected
resistor string. Thus, only the maximum and minimum gamma voltages
GVmax and GVmin are applied to the first and second polarity
selectors 151 and 152 regardless of the polarity selection signal
pss. That is, the input signals of the first and second polarity
selectors 151 and 152 do not swing according to the polarity
selection signal pss.
[0039] The gamma selection buffers GSB1 to GSB9 buffer the
corresponding gamma voltages GV1 to GV9, select one of the positive
resistor string PR-ST and the negative resistor string NR-ST in
response to the polarity selection signal pss, and apply the
buffered gamma voltages GV1 to GV9 to the corresponding nodes among
a plurality of nodes between a plurality of resistors of the
selected resistor string.
[0040] The positive grayscale voltages VP0 to VP63 are output
through a plurality of nodes of the positive resistor string PR-ST,
and the negative grayscale voltages VN0 to VN63 are output through
a plurality of nodes of the negative resistor string NR-ST. Nodes
in the positive resistor string PR-ST and the negative resistor
string NR-ST to which the gamma voltages GV1 to GV9 are applied are
fixed by the gamma characteristic curve of the positive and
negative grayscale voltages VP0 to VP63 and VN0 to VN63 to be
output. Since the voltages of the nodes in the positive resistor
string PR-ST and the negative resistor string NR-ST to which the
gamma voltages GV1 to GV9 are applied are fixed by the gamma
voltages GV1 to GV9, a voltage is divided by at least one resistor
and applied to a node between the nodes in the positive resistor
string PR-ST and the negative resistor string NR-ST to which the
gamma voltages GV1 to GV9 are applied.
[0041] As illustrated in FIG. 1, when the fifth gamma selection
buffer GSB5 disposed in the middle of the first to ninth gamma
selection buffers GSB1 to GSB9 outputs a medium positive grayscale
voltage VPC that is between the first positive grayscale voltage
VP0 and the sixty-fourth positive grayscale voltage VP63, the fifth
gamma selection buffer GSB5 may output a medium negative grayscale
voltage VNC that is between the first negative grayscale voltage
VN0 and the sixty-fourth negative grayscale voltage VN63 because
the positive resistor string PR-ST and the negative resistor string
NR-ST are symmetrical to each other. Also, the gamma selection
buffers GSB1 to GSB9 may indicate positions that do not correspond
to each other in the positive and negative resistor strings PR-ST
and NR-ST. For example, even if the first gamma selection buffer
GSB1 outputs the sixty-third positive grayscale voltage VP62, the
first gamma selection buffer GSB1 may not output the second
negative grayscale voltage VN1 corresponding to the sixty-third
positive grayscale voltage VP62 but may output the third negative
grayscale voltage VN2. In other words, positive and negative
grayscale voltages output by each of the gamma selection buffers
GSB1 to GSB9 may be adjusted according to the gamma characteristic
curve of the display panel.
[0042] Here, either of the resistors of the positive resistor
string PR-ST or the resistors of the negative resistor string NR-ST
may not have the same resistance in consideration of the gamma
characteristic curve. However, when the resistors of the positive
resistor string PR-ST have the same resistance, the negative
resistor string NR-ST may be configured to be the same as the
positive resistor string PR-ST. The positive and negative resistor
strings PR-ST and NR-ST may be classified as a resistor string unit
and disposed out of the gamma voltage selector 150.
[0043] The grayscale voltage selector 155 selects one of the
positive grayscale voltages VP0 to VP63 applied from the positive
resistor string PR-ST or the negative grayscale voltages VN0 to
VN63 applied from the negative resistor string NR-ST in response to
the polarity selection signal pss, and outputs a selection
grayscale voltage GSV. In other words, the grayscale voltage
selector 155 may output one of symmetrical grayscale voltages VP0
to VP63 or VN0 to VN63 in response to the polarity selection signal
pss.
[0044] Thus, the above-described display driver circuit 100 of FIG.
1 may output the positive grayscale voltages VP0 to VP63 and the
negative grayscale voltages VN0 to VN63 corresponding to the
positive grayscale voltages VP0 to VP63 in response to the polarity
signal PS. Also, even if the display driver circuit 100 alternately
outputs the positive and negative grayscale voltages VP0 to VP63
and VN0 to VN63, the gamma voltages GVmax, GVmin, and GV1 to GV9 do
not vary, and thus the first and second reference buffers 123 and
124, the first and second polarity selectors 151 and 152, and first
to ninth gamma selection buffers GSB1 to GSB9 do not swing output
or input signals. Consequently, a delay in outputting the
symmetrical grayscale voltages VP0 to VP63 and VN0 to VN63 is very
short, and it is possible to generate the symmetrical grayscale
voltages VP0 to VP63 and VN0 to VN63 at high speed.
[0045] Although not shown, the display driver circuit 100 of FIG. 1
may additionally include a common voltage generator for generating
a common voltage applied to a common electrode (not shown). A
display driver circuit using the method of inverting the polarity
of a pixel electrode may have to apply the positive and negative
grayscale voltages VP0 to VP63 and VN0 to VN63 to a pixel electrode
and also a first common voltage corresponding to the positive
grayscale voltages VP0 to VP63 and a second common voltage
corresponding to the negative grayscale voltages VN0 to VN63 to the
common electrode. In this case, the common voltage generator (not
shown) may generate the first and second common voltages in
response to the polarity selection signal pss.
[0046] FIG. 2 is a grayscale voltage (V)-transmissivity (T) graph
showing the relationship between grayscale voltage and
transmissivity to describe symmetrical grayscale voltages generated
from the display driver circuit of FIG. 1.
[0047] Symmetrical grayscale voltages of FIG. 2 will now be
described with reference to FIG. 1. As illustrated in FIG. 2, the
positive grayscale voltages VP0 to VP63 in a positive grayscale
voltage characteristic curve VP increase as transmissivity
increases, while the negative grayscale voltages VN0 to VN63 in a
negative grayscale voltage characteristic curve VN decrease as
transmissivity increases. The first positive grayscale voltage VP0
and the sixty-fourth negative grayscale voltage VN63 are the same
as the minimum gamma voltage GVmin, and the first negative
grayscale voltage VN0 and the sixty-fourth positive grayscale
voltage VP63 are the same as the maximum gamma voltage GVmax. Also,
the medium positive grayscale voltage VPC and the medium negative
grayscale voltage VNC are the same. The positive and negative
grayscale voltage characteristic curves VP and VN are symmetrical
with respect to the medium positive grayscale voltage VPC and the
medium negative grayscale voltage VNC.
[0048] A first common voltage Vcom1 is lower than the first
positive grayscale voltage VP0 and the sixty-fourth negative
grayscale voltage VN63 by a predetermined amount (e.g., 0.3 V), and
a second common voltage Vcom2 is higher than the first negative
grayscale voltage VN0 and the sixty-fourth positive grayscale
voltage VP63 by a predetermined amount (e.g., 0.3 V). A difference
between the first common voltage Vcom1 and the first positive
grayscale voltage VP0 may be set to be the same as a difference
between the second common voltage Vcom2 and the first negative
grayscale voltage VN0. In other words, differences between the
first or second common voltage Vcom1 or Vcom2 applied to the common
electrode and the positive or negative grayscale voltages VP0 to
VP63 or VN0 to VN63 applied to a pixel electrode have the same
absolute value and opposite polarities, so that electric fields are
applied between the common electrode and the pixel electrode in
opposite directions. However, since the voltage differences have
the same absolute value, the same electric fields are applied to a
liquid crystal layer, and the liquid crystal layer has the same
transmissivity.
[0049] FIG. 3 is a circuit diagram of an example of a gamma
selection buffer shown in FIG. 1.
[0050] Each of the gamma selection buffers GSB1 to GSB9 may include
a first amplifier FA21, second amplifiers SA21 to SA22, and a
switch CSW.
[0051] In the exemplary gamma selection buffer shown in FIG. 3, the
switch CSW performs a switching operation in response to the
polarity selection signal pss so that the first amplifier FA21 is
connected with one of the second amplifiers SA21 and SA22. Each of
the second amplifiers SA21 and SA22 is connected with the
corresponding one of a plurality of nodes in the positive resistor
string PR-ST or the negative resistor string NR-ST. The first
amplifier FA21 amplifies a difference between a gamma voltage GV
output from the corresponding one of the gamma selectors GS1 to GS9
in the gamma selection unit 153 and an output VP or VN fed back
from a selected one of the second amplifiers SA21 and SA22, and
outputs the amplified difference to the selected one of the second
amplifiers SA21 and SA22. One of the second amplifiers SA21 and
SA22 selected by the switch CSW buffers the output of the first
amplifier FA21 and outputs the buffered grayscale voltage VP or VN
to the corresponding node in the positive resistor string PR-ST or
the negative resistor string NR-ST. For example, when the switch
CSW selects the second amplifier SA21 in response to the polarity
selection signal pss, the first amplifier FA21 amplifies a
difference between the positive grayscale voltage VP output from
the second amplifier SA21 and the gamma voltage GV applied from the
corresponding gamma selector, and outputs the amplified voltage
difference to the selected second amplifier SA21. Then, the
selected second amplifier SA21 buffers the voltage applied from the
first amplifier FA21 and outputs the buffered voltage to the
corresponding node in the connected positive resistor string
PR-ST.
[0052] FIG. 4 is a block diagram of a display device according to
an exemplary embodiment.
[0053] Referring to FIG. 4, the display device includes a grayscale
voltage generator 100, a source driver 200, a controller 300, and a
gate driver 400, and a panel 500.
[0054] The grayscale voltage generator 100 generates positive
grayscale voltages VP0 to VP63 or negative grayscale voltages VN0
to VN63 in response to a polarity signal PS applied from the
controller 300, and provides one of the generated positive
grayscale voltages VP0 to VP63 or negative grayscale voltages VN0
to VN63 to the source driver 200 as a selection grayscale voltage
GSV. The source driver 200 receives the selection grayscale voltage
GSV in response to a source driver control signal CS1 applied from
the controller 300, and applies a display data voltage PDS to the
data lines of the panel 500. The gate driver 400 applies a gate-on
voltage GOS to the gate lines of the panel 500 in response to a
gate driver control signal CS2 applied from the controller 300,
thereby driving the display panel 500. The controller 300 provides
the source driver control signal CS1 to the source driver 200 and
the gate driver control signal CS2 to the gate driver 400 in
response to image data G-data and a command com applied from the
outside, thereby controlling the gate driver 400 and the source
driver 200. Also, the controller 300 applies the polarity signal PS
to the grayscale voltage generator 100 according to the method of
inverting the polarity of a pixel electrode so that one of the
positive grayscale voltages VP0 to VP63 or the negative grayscale
voltages VN0 to VN63 is output to the source driver 200 as the
selection grayscale voltage GSV.
[0055] As described above, in a display driver circuit according to
one or more exemplary embodiments, a grayscale voltage generator
may have symmetrically formed positive and negative resistor
strings, and may apply the maximum and minimum gamma voltages to
one of the positive and negative resistor strings in response to a
polarity selection signal, thereby generating a plurality of
positive grayscale voltages or a plurality of negative grayscale
voltages without changing the gamma voltages. Even if the polarity
of a grayscale voltage is changed, the grayscale voltage generator
does not change a gamma voltage and thus can generate symmetrical
grayscale voltages at high speed and low power consumption.
[0056] The foregoing is illustrative of exemplary embodiments and
is not to be construed as limiting thereof. Although a few
exemplary embodiments have been described, those skilled in the art
will readily appreciate that many modifications are possible in the
exemplary embodiments without materially departing from the novel
teachings and aspects. Accordingly, all such modifications are
intended to be included within the scope of this inventive concept
as defined in the claims. For example, exemplary embodiments can be
applied to a measurement method for monitoring process variation in
semiconductor equipment. In the claims, means-plus-function clauses
are intended to cover the structures described herein as performing
the recited function, and not only structural equivalents but also
equivalent structures. Therefore, it is to be understood that the
foregoing is illustrative of various exemplary embodiments and is
not to be construed as limited to the specific embodiments
disclosed, and that modifications to the disclosed embodiments, as
well as other embodiments, are intended to be included within the
scope of the appended claims.
* * * * *